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gh-129752: Don't update adaptive counters when TLBC=0 in free-threading. #155497

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gh-129752: Don't update adaptive counters when TLBC=0 in free-threading. #155497

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6 changes: 6 additions & 0 deletions Include/internal/pycore_backoff.h
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,12 @@ backoff_counter_triggers(_Py_BackoffCounter counter)
return counter.value_and_backoff < UNREACHABLE_BACKOFF;
}

static inline bool
backoff_counter_is_unreachable(_Py_BackoffCounter counter)
{
return (counter.value_and_backoff & BACKOFF_MASK) == UNREACHABLE_BACKOFF;
}

static inline _Py_BackoffCounter
trigger_backoff_counter(void)
{
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1 change: 0 additions & 1 deletion Lib/test/test_thread_local_bytecode.py
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Expand Up @@ -108,7 +108,6 @@ def f(a, b, q=None):
""")
assert_python_ok("-X", "tlbc=1", "-c", code)

@support.skip_if_sanitizer("gh-129752: data race on adaptive counter", thread=True)
def test_no_copies_if_tlbc_disabled(self):
code = textwrap.dedent("""
import queue
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-08-11-01-45-24.gh-issue-129752.Zo3OUx.rst
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@@ -0,0 +1,2 @@
Don't update adaptive counters in the free-threaded build when thread-local
bytecode is disabled (``-X tlbc=0``). Patch by Donghee Na.
18 changes: 18 additions & 0 deletions Python/ceval_macros.h
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Expand Up @@ -354,6 +354,23 @@ static void dtrace_function_return(_PyInterpreterFrame *);
#define ADAPTIVE_COUNTER_TRIGGERS(COUNTER) \
backoff_counter_triggers(forge_backoff_counter((COUNTER)))

#ifdef Py_GIL_DISABLED
/* Counters are unreachable when thread-local bytecode is disabled,
* so there is no need to update them. */
#define ADVANCE_ADAPTIVE_COUNTER(COUNTER) \
do { \
if (!backoff_counter_is_unreachable((COUNTER))) { \
(COUNTER) = advance_backoff_counter((COUNTER)); \
} \
} while (0);

#define PAUSE_ADAPTIVE_COUNTER(COUNTER) \
do { \
if (!backoff_counter_is_unreachable((COUNTER))) { \
(COUNTER) = pause_backoff_counter((COUNTER)); \
} \
} while (0);
#else
#define ADVANCE_ADAPTIVE_COUNTER(COUNTER) \
do { \
(COUNTER) = advance_backoff_counter((COUNTER)); \
Expand All @@ -363,6 +380,7 @@ static void dtrace_function_return(_PyInterpreterFrame *);
do { \
(COUNTER) = pause_backoff_counter((COUNTER)); \
} while (0);
#endif

#ifdef ENABLE_SPECIALIZATION
/* Multiple threads may execute these concurrently if thread-local bytecode is
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